Redundant storage devices such as a RAID device composed of plural disks disconnect a disk involving any failure in the event of disk failure. Here, the disk failure refers to, for example, thermal off-track, contamination, noise, a contact failure, etc.
Such a storage device disconnects a disk involving any failure and updates recorded data using normal disks only. If a failure occurs in another disk, the storage device additionally disconnects the disk involving a failure. Such a state that a failure occurs in plural disks and redundancy is lost and in addition, a disk is further disconnected is called a multi-dead state. Here, the disk disconnected due to the failure occurrence can temporarily operate a normal disk as a result of hard reset or power restore. This is because a disk is disconnected due to temporal noise contamination, thermal off-track, and a small foreign material (contamination) on a medium in the disk in many cases, and often recovers as a result of restoring a power after power-off, hard reset, or the like. To that end, the disconnected disk is hard-reset or a power is restored for the disconnected disk in order to restore the storage device from the multi-dead state to a status just before the elimination of redundancy. Then, the disconnected disk is driven and set to the status just before the elimination of redundancy. However, if states of plural disks just before elimination of redundancy cannot be securely determined, in the case of rebooting the storage device, a system might fail to start or erroneously operate due to erroneous write to any disk. To elaborate, the following problem occurs; if disks cannot be prioritized and reconnected upon recovery of plural disconnected disks, states of the disks just before elimination of redundancy cannot be securely determined.
Further, a disk array control device capable of restoring a disk device is disclosed in the Japanese Laid-open Patent Publication No. 10-289065